Method and apparatus for transmitting overload indicatior over the air

ABSTRACT

Techniques for transmitting overload indicators over the air to UEs in neighbor cells are described. In one design, an overload indicator may be transmitted as a phase difference between at least one synchronization signal and a reference signal for a cell. In another design, an overload indicator may be transmitted as a phase difference between consecutive transmissions of at least one synchronization signal for a cell. In yet another design, an overload indicator may be transmitted by a cell on resources reserved for transmitting the overload indicator. In yet another design, an overload indicator may be transmitted by a cell on a low reuse channel or a broadcast channel. For all designs, a UE may receive overload indicators from neighbor cells, determine the loading of each neighbor cell based on the overload indicator for that cell, and control its operation based on the loading of the neighbor cells.

This is a divisional application of U.S. patent application Ser. No.12/686,260, entitled “METHOD AND APPARATUS FOR TRANSMITTING OVERLOADINDICATOR OVER THE AIR,” filed Jan. 12, 2010, assigned U.S. Pat. No.8,982,750 with an issue date of Mar. 17, 2015, which claims priority toprovisional U.S. Application Ser. No. 61/145,428, entitled “Method andApparatus to Support an Over-the-Air (OTA) Load Indicator,” filed Jan.16, 2009, and provisional U.S. Application Ser. No. 61/159,607, entitled“OVER-THE-AIR OVERLOAD INDICATOR,” filed Mar. 12, 2009, all of which areassigned to the assignee hereof and incorporated herein by reference.

BACKGROUND

I. Field

The present disclosure relates generally to communication, and morespecifically to techniques for transmitting information in a wirelesscommunication system.

II. Background

Wireless communication systems are widely deployed to provide variouscommunication content such as voice, video, packet data, messaging,broadcast, etc. These wireless systems may be multiple-access systemscapable of supporting multiple users by sharing the available systemresources. Examples of such multiple-access systems include CodeDivision Multiple Access (CDMA) systems, Time Division Multiple Access(TDMA) systems, Frequency Division Multiple Access (FDMA) systems,Orthogonal FDMA (OFDMA) systems, and Single-Carrier FDMA (SC-FDMA)systems.

A wireless communication system may include a number of base stationsthat can support communication for a number of user equipments (UEs). Abase station may concurrently communicate with multiple UEs via thedownlink and the uplink. The downlink (or forward link) refers to thecommunication link from the base station to the UEs, and the uplink (orreverse link) refers to the communication link from the UEs to the basestation. On the uplink, each UE may transmit data and/or otherinformation to its serving base station, and the transmission from theUE may cause interference to neighbor base stations. It may be desirableto mitigate interference in order to improve system performance.

SUMMARY

Techniques for transmitting overload indicators over the air to UEs inneighbor cells to manage interference and improve system performance aredescribed herein. An overload indicator for a cell may comprise varioustype of information that may be used to support system operation andimprove performance. For example, the overload indicator may indicatethe loading of the cell, e.g., whether the cell is observing heavyloading.

In a first design, an overload indicator may be transmitted as a phasedifference between at least one synchronization signal and a referencesignal for a cell. The cell may determine the overload indicator basedon its loading. The cell may transmit the reference signal, which may beused by UEs for channel estimation and/or other purposes. The cell mayalso transmit the at least one synchronization signal, which may be usedby UEs for cell acquisition and/or other purposes. The overloadindicator may be transmitted on the at least one synchronization signal,and the reference signal may be used as a phase reference.

In a second design, an overload indicator may be transmitted as a phasedifference between consecutive transmissions of at least onesynchronization signal for a cell. The cell may determine the overloadindicator based on its loading. The cell may send a first transmissionof the at least one synchronization signal in a first time period. Thecell may also send a second transmission of the at least onesynchronization signal comprising the overload indicator in a secondtime period. The overload indicator may be conveyed by a phasedifference between the second transmission and the first transmission ofthe at least one synchronization signal.

In a third design, an overload indicator may be transmitted by a cell onresources reserved for transmitting the overload indicator. The cell maydetermine the overload indicator based on its loading. The cell maydetermine resources reserved for transmitting the overload indicator.The reserved resources may comprise resource elements in a data regionof at least one resource block, resource elements in a control region ofat least one resource block, unused resource elements in at least oneresource block, and/or other resource elements. The cell may transmitthe overload indicator on the reserved resources to UEs in neighborcells.

In a fourth design, an overload indicator may be transmitted by a cellon a low reuse channel or a broadcast channel. The cell may determinethe overload indicator based on its loading. The cell may transmit theoverload indicator on the low reuse channel (which may observe lessinterference from neighbor cells) or on the broadcast channel to UEs inneighbor cells. The cell may also transmit at least one overloadindicator for at least one neighbor cell on the low reuse channel or thebroadcast channel to its UEs.

An overload indicator may also be transmitted over the air in othermanners. For all designs, a UE may receive one or more overloadindicators from one or more neighbor cells. The UE may perform detectionfor the overload indicators in a manner dependent on how the overloadindicators are transmitted by the neighbor cells. The UE may determinethe loading of each neighbor cell based on the overload indicator forthat neighbor cell. The UE may control its operation based on theloading of the neighbor cells. The UE may also determine feedbackinformation based on the overload indicators and may send the feedbackinformation to the serving cell.

Various aspects and features of the disclosure are described in furtherdetail below.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a wireless communication system.

FIG. 2 shows an exemplary frame structure.

FIG. 3 shows two exemplary subframe formats.

FIG. 4 shows a design of over-the-air transmission of overloadindicators.

FIGS. 5A and 5B show two designs of reserving resources in a data regionof a resource block pair for transmitting an overload indicator.

FIGS. 6A and 6B show two designs of reserving unused resource elementsfor transmitting an overload indicator.

FIGS. 7, 9, 11 and 13 show processes for transmitting an overloadindicator based on the first, second, third and fourth designs,respectively.

FIGS. 8, 10, 12 and 14 show apparatuses for transmitting an overloadindicator based on the first, second, third and fourth designs,respectively.

FIGS. 15, 17, 19 and 21 show processes for receiving an overloadindicator transmitted based on the first, second, third and fourthdesigns, respectively.

FIGS. 16, 18, 20 and 22 show apparatuses for receiving an overloadindicator transmitted based on the first, second, third and fourthdesigns, respectively.

FIG. 23 shows a block diagram of a UE and two base stations.

DETAILED DESCRIPTION

The techniques described herein may be used for various wirelesscommunication systems such as CDMA, TDMA, FDMA, OFDMA, SC-FDMA and othersystems. The terms “system” and “network” are often usedinterchangeably. A CDMA system may implement a radio technology such asUniversal Terrestrial Radio Access (UTRA), cdma2000, etc. UTRA includesWideband CDMA (WCDMA) and other variants of CDMA. cdma2000 coversIS-2000, IS-95 and IS-856 standards. A TDMA system may implement a radiotechnology such as Global System for Mobile Communications (GSM). AnOFDMA system may implement a radio technology such as Evolved UTRA(E-UTRA), Ultra Mobile Broadband (UMB), IEEE 802.11 (Wi-Fi), IEEE 802.16(WiMAX), IEEE 802.20, Flash-OFDM®, etc. UTRA and E-UTRA are part ofUniversal Mobile Telecommunication System (UMTS). 3GPP Long TermEvolution (LTE) and LTE-Advanced (LTE-A) are new releases of UMTS thatuse E-UTRA, which employs OFDMA on the downlink and SC-FDMA on theuplink. UTRA, E-UTRA, UMTS, LTE, LTE-A and GSM are described indocuments from an organization named “3rd Generation PartnershipProject” (3GPP). cdma2000 and UMB are described in documents from anorganization named “3rd Generation Partnership Project 2” (3GPP2). Thetechniques described herein may be used for the systems and radiotechnologies mentioned above as well as other systems and radiotechnologies. For clarity, certain aspects of the techniques aredescribed below for LTE, and LTE terminology is used in much of thedescription below.

FIG. 1 shows a wireless communication system 100, which may be an LTEsystem or some other system. System 100 may include a number of evolvedNode Bs (eNBs) 110 and other network entities. An eNB may be a stationthat communicates with the UEs and may also be referred to as a basestation, a Node B, an access point, etc. Each eNB 110 may providecommunication coverage for a particular geographic area. To improvecapacity, the overall coverage area of an eNB may be partitioned intomultiple (e.g., three) smaller areas. In 3GPP, the term “cell” can referto the smallest coverage area of an eNB and/or an eNB subsystem servingthis coverage area, depending on the context in which the term is used.

An eNB may provide communication coverage for a macro cell, a pico cell,a femto cell, and/or other types of cell. A macro cell may cover arelatively large geographic area (e.g., several kilometers in radius)and may allow unrestricted access by UEs with service subscription. Apico cell may cover a relatively small geographic area and may allowunrestricted access by UEs with service subscription. A femto cell maycover a relatively small geographic area (e.g., a home) and may allowrestricted access by UEs having association with the femto cell (e.g.,UEs in a Closed Subscriber Group (CSG)). In the example shown in FIG. 1,eNBs 110 a, 110 b and 110 c may be macro eNBs for macro cells 102 a, 102b and 102 c, respectively. eNB 110 d may be a pico eNB for a pico cell102 d. eNB 110 e may be a femto eNB for a femto cell 102 e. The terms“cell”, “eNB”, and “base station” may be used interchangeably.

A network controller 130 may couple to a set of eNBs and may providecoordination and control for these eNBs. Network controller 130 maycommunicate with eNBs 110 via a backhaul. eNBs 110 may also communicatewith one another, e.g., directly or indirectly via wireless or wirelinebackhaul.

System 100 may be a synchronous system or an asynchronous system. For asynchronous system, the eNBs may have similar frame timing, andtransmissions from different eNBs may be approximately aligned in time.For an asynchronous system, the eNBs may have different frame timing,and transmissions from different eNBs may not be aligned in time.

UEs 120 may be dispersed throughout system 100, and each UE may bestationary or mobile. A UE may also be referred to as a terminal, amobile station, a subscriber unit, a station, etc. A UE may be acellular phone, a personal digital assistant (PDA), a wireless modem, awireless communication device, a handheld device, a laptop computer, acordless phone, a wireless local loop (WLL) station, etc. A UE maycommunicate with a cell via the downlink and uplink. In FIG. 1, a solidline with double arrows indicates desired transmissions between a UE anda serving cell, which is a cell designated to serve the UE. A dashedline with double arrows indicates interfering transmissions between a UEand a neighbor cell, which is a cell not serving the UE.

LTE utilizes orthogonal frequency division multiplexing (OFDM) on thedownlink and single-carrier frequency division multiplexing (SC-FDM) onthe uplink. OFDM and SC-FDM partition a frequency range into multiple(N_(FFT)) orthogonal subcarriers, which are also commonly referred to astones, bins, etc. Each subcarrier may be modulated with data. Ingeneral, modulation symbols are sent in the frequency domain with OFDMand in the time domain with SC-FDM. The spacing between adjacentsubcarriers may be fixed, and the total number of subcarriers (N_(FFT))may be dependent on the system bandwidth. For example, N_(FFT) may beequal to 128, 256, 512, 1024 or 2048 for system bandwidth of 1.25, 2.5,5, 10 or 20 megahertz (MHz), respectively.

FIG. 2 shows an exemplary frame structure 200 used for the downlink inLTE. The transmission timeline for the downlink may be partitioned intounits of radio frames. Each radio frame may have a predeterminedduration (e.g., 10 milliseconds (ms)) and may be partitioned into 10subframes with indices of 0 through 9. Each subframe may include twoslots. Each radio frame may thus include 20 slots with indices of 0through 19. Each slot may include L symbol periods, e.g., seven symbolperiods for a normal cyclic prefix (as shown in FIG. 2) or six symbolperiods for an extended cyclic prefix. The 2L symbol periods in eachsubframe may be assigned indices of 0 through 2L−1.

In LTE, each cell may transmit a primary synchronization signal (PSS)and a secondary synchronization signal (SSS) on the downlink. Forfrequency division duplexing (FDD) in LTE, which is shown in FIG. 2, thePSS and SSS may be transmitted in symbol periods 6 and 5, respectively,in each of subframes 0 and 5 of each radio frame with the normal cyclicprefix, as shown in FIG. 2. The PSS and SSS may be used by UEs for cellacquisition. Each cell may also transmit a Physical Broadcast Channel(PBCH) in symbol periods 0 to 3 in slot 1 of subframe 0. The PBCH maycarry certain system information. Each cell may transmit the PSS, SSSand PBCH in the center 1.08 MHz of the system bandwidth and may sendother transmissions in the remaining part of the system bandwidth.

The PSS, SSS, and PBCH in LTE are described in 3GPP TS 36.211, entitled“Evolved Universal Terrestrial Radio Access (E-UTRA); Physical Channelsand Modulation,” which is publicly available.

FIG. 3 shows two exemplary regular subframe formats 310 and 320 for thedownlink for the normal cyclic prefix. The available time frequencyresources for the downlink may be partitioned into resource blocks. Eachresource block may cover 12 subcarriers in one slot and may include anumber of resource elements. Each resource element may cover onesubcarrier in one symbol period and may be used to send one modulationsymbol, which may be a real or complex value.

As shown in FIG. 3, a subframe may include a control region followed bya data region. The control region may include the first M OFDM symbolsof the subframe, where M may be equal to 1, 2, 3 or 4. M may change fromsubframe to subframe and may be conveyed by a Physical Control FormatIndicator Channel (PCFICH) that is sent in the first symbol period ofthe subframe. The first M OFDM symbols may be TDM control symbols, whichare OFDM symbols carrying control information. The data region mayinclude the remaining 2L−M symbol periods of the subframe and may carrydata for UEs. In the example shown in FIG. 3, each subframe includesthree TDM control symbols with M=3. Control information may be sent insymbol periods 0 to 2, and data may be sent in the remaining symbolperiods 3 to 13 of the subframe.

A cell may transmit a Physical HARQ Indicator Channel (PHICH) and aPhysical Downlink Control Channel (PDCCH) in the control region. ThePHICH may carry information to support hybrid automatic retransmission(HARQ). The PDCCH may carry information on resource allocation for UEsand control information for downlink channels. The cell may transmit aPhysical Downlink Shared Channel (PDSCH) in the data region. The PDSCHmay carry data for UEs scheduled for data transmission on the downlink.The various channels in LTE are described in the aforementioned 3GPP TS36.211.

Subframe format 310 may be used for an eNB equipped with two antennas. Acell-specific reference signal (RS) may be transmitted in symbol periods0, 4, 7 and 11 and may be used by UEs for channel estimation and othermeasurements. A reference signal is a signal that is known a priori by atransmitter and a receiver and may also be referred to as pilot. Acell-specific reference signal is a reference signal that is specificfor a cell, e.g., generated based on a cell identity (ID). In FIG. 3,for a given resource element with label R_(a), a reference symbol may betransmitted on that resource element from antenna a, and no modulationsymbols may be transmitted on that resource element from other antennas.Subframe format 320 may be used by an eNB equipped with four antennas.The RS may be transmitted in symbol periods 0, 1, 4, 7, 8 and 11. Forboth subframe formats 310 and 320, resource elements not used for the RS(shown without shading in FIG. 3) may be used to transmit data and/orcontrol information.

In an aspect, a cell may transmit an overload indicator over the air toUEs in neighbor cells. An overload indicator (OI) may also be referredto as a load indicator (LI), an other sector interference (OSI)indicator, etc. The overload indicator may be used to control operationof the UEs to improve system performance.

FIG. 4 shows a design of over-the-air (OTA) transmission of overloadindicators. For simplicity, FIG. 4 shows a UE communicating with aserving cell and having two neighbor cells. In general, a UE may haveany number of neighbor cells. As shown in FIG. 4, the UE may communicatewith the serving cell, may receive downlink transmission from theserving cell, and may send uplink transmission to the serving cell. Theuplink transmission from the UE may cause interference to the neighborcells. The UE may also receive an overload indicator from each neighborcell. The UE may control its operation based on the overload indicatorsreceived from the neighbor cells. Alternatively or additionally, the UEmay generate feedback information based on the overload indicators andmay send the feedback information to the serving cell.

In general, an overload indicator for a cell may comprise anyinformation that may be used to support system operation and improveperformance. In one design, the overload indicator may indicate theloading of the cell. For example, the overload indicator may comprise asingle bit that may be set to either a first value (e.g., 0) to indicatelight loading or a second value (e.g., 1) to indicate heavy loading. Theoverload indicator may also comprise more bits, which may be used toconvey more loading levels. In another design, the overload indicatormay indicate the amount of resources and/or the specific resources usedby the cell. The overload indicator may also comprise other informationindicative of loading of the cell.

In one design, an overload indicator may convey loading of a cell forthe entire system bandwidth. In other designs, an overload indicator mayconvey loading for a specific subband or frequency range, or a specifictime interval, or specific time-frequency resources, etc.

An overload indicator may be used for various purposes. In one design,an overload indicator may be used for interference management. A cellmay communicate with a number of UEs served by the cell (which may bereferred to as the served UEs). The cell may observe interference fromother UEs communicating with neighbor cells (which may be referred to asthe neighbor UEs). The served UEs may also cause interference to theneighbor cells. The interference may degrade performance.

For interference management, a cell may transmit an overload indicatorto the neighbor UEs. These UEs may control their operation based on theoverload indicator from the cell. A given UE may receive overloadindicators from neighbor cells and may control its operation based onthese overload indicators. In a first design, the UE may reduce itstransmit power, skip certain transmission, avoid using certainresources, and/or perform other actions if the overload indicator fromany neighbor cell indicates heavy loading at that neighbor cell. In asecond design, the UE may report the overload indicators from theneighbor cells to the serving cell. In a third design, the UE maycompute a transmit power level that it should use based on the receivedoverload indicators and may report this transmit power level to theserving cell. For the second and third designs, the serving cell maytake corrective actions based on the feedback information (e.g., theoverload indicators or the transmit power level) received from the UEand possibly other information (e.g., the pilot measurement reports fromthe UE) in order to reduce interference caused by the UE to the neighborcells. For example, the serving cell may use this information for powercontrol of the UE and in scheduling the UE.

An overload indicator may be intended for UEs in neighbor cells and maybe transmitted such that it can be reliably received by these UEs. Theoverload indicator may also be received and used by the UEs in the cell.The overload indicator may be transmitted periodically (e.g., with aperiodicity in a range of 5 to 30 ms) in order to timely convey changesin loading of the cell. The overload indicator may be transmitted on anoverload indicator channel (OICH) in various manners.

In a first OICH design, an overload indicator may be transmitted as aphase difference between the PSS and/or SSS and the RS for a cell. TheRS may be used as a reference phase. The overload indicator may betransmitted by varying the phase of the PSS and/or SSS relative to thereference phase. In general, the overload indicator may be transmittedon the PSS and/or the SSS. In the description below, “PSS/SSS” can referto only the PSS, or only the SSS, or both the PSS and SSS.

The RS for the cell may be generated as follows. A reference signalsequence may be generated based on a pseudo-random sequence, which maybe initialized based on the cell ID of the cell. The reference signalsequence may be mapped to a set of resource elements in an OFDM symbolcarrying the RS. The set of resource elements may occupy subcarriersselected based on the cell ID and spaced apart by six subcarriers, asshown in FIG. 3.

The PSS for the cell may be generated as follows. A PSS sequence may begenerated based on a Zadoff-Chu sequence, which may in turn be generatedbased on the cell ID of the cell. The PSS sequence may be mapped to 31resource elements on each side of a center/DC subcarrier in an OFDMsymbol carrying the PSS. The PSS may thus be generated based on the cellID and transmitted in the center 945 KHz of the system bandwidth.

The SSS for the cell may be generated as follows. A set of pseudo-randomsequences and scrambling sequences may be generated based on the cell IDof the cell. An SSS sequence may then be generated based on the set ofpseudo-random sequences and scrambling sequences. The SSS sequence maybe mapped to 31 resource elements on each side of the center/DCsubcarrier in an OFDM symbol carrying the SSS. The SSS may thus begenerated based on the cell ID and transmitted in the center 945 KHz ofthe system bandwidth.

The RS may be transmitted from only one physical antenna (or one antennaport) on any given resource element, e.g., as shown in FIG. 3. A UE canestimate the channel response from each physical antenna for the cell tothe UE based on the RS transmitted from that physical antenna.

The PSS and SSS may be transmitted from a virtual antenna formed by alinear combination of T physical antennas for the cell, where T may begreater than one. In general, any set of weights may be used for thelinear combination of the T physical antennas, and the selected weightsform a beam for the PSS and SSS. The same beam may be used for onetransmission/instance of the PSS and SSS sent the same subframe for FDDin LTE. However, the beam may change over time (e.g., different beamsmay be used for different transmissions of the PSS and SSS) to obtainspatial diversity. The UEs can receive the PSS and SSS without knowingthe beams. However, when an overload indicator is transmitted as a phasedifference between the PSS/SSS and the RS, the beam or weights may bespecified or conveyed to the UEs to allow the UEs to recover theoverload indicator. The UEs can then use the RS as a phase reference fora symbol carrying the overload indicator and modulated as a phase on thePSS/SSS

The overload indicator may be transmitted in the PSS and/or the SSS. InLTE, there are three possible PSS sequences and 168 possible SSSsequences for a total of 504 cell IDs. Each cell transmits one PSSsequence and one SSS sequence determined based on its cell ID. Thelikelihood of multiple cells transmitting the same PSS sequence may bemuch greater than the likelihood of multiple cells transmitting the sameSSS sequence. Hence, better performance may be obtained by transmittingthe overload indicator in the SSS and performing detection for theoverload indicator based on the SSS.

In one design, the overload indicator may be transmitted on the PSS orSSS as follows. A set of 62 symbols may be generated for the PSS or SSS,and each symbol may be a real or complex value. Each of the 62 symbolsmay be multiplied with a symbol for the overload indicator, as follows:

B(k)=X·A(k),  Eq (1)

where

A(k) is a symbol for the PSS or SSS for subcarrier k,

X is a symbol for the overload indicator, and

B(k) is a modulated symbol for carrier k.

The symbol for the overload indicator may be a BPSK symbol carrying oneinformation bit, a QPSK symbol carrying two information bits, etc. Asshown in equation (1), the 62 symbols for the PSS or SSS may bemultiplied with the same symbol for the overload indicator to obtain 62modulated symbols, which may be mapped to the 62 subcarriers used forthe PSS or SSS.

Precoding may be performed with a set of weights to transmit themodulated symbols along a beam, as follows:

X(k)=W·B(k),  Eq (2)

where

-   -   W=[W₁ . . . W_(T)]^(T) is a vector of weights for the T physical        antennas,    -   X(k)=[X₁(k) . . . X_(T)(k)]^(T) is a vector of output symbols        for the T physical antennas on subcarrier k, and    -   “^(T)” denotes a transpose.

As shown in equation (2), precoding may be performed to transmit along abeam formed by a linear combination of physical antennas. Precoding maybe omitted to transmit directly from the physical antennas without abeam. Precoding may also be performed in other manners, e.g., on OFDMsymbols instead of on modulated symbols. One set of 62 output symbolsmay be generated for each physical antenna by the precoding shown inequation (2). An OFDM symbol may be generated for each physical antennawith the 62 output symbols for that physical antenna mapped to the 62subcarriers used for the PSS or SSS and possibly other symbols mapped toother subcarriers. Each OFDM symbol may be transmitted from its physicalantenna.

A UE may receive the PSS or SSS from the cell. The received symbols forthe PSS or SSS (assuming one antenna at the UE) may be expressed as:

Y(k)=H ₁(k)·W ₁ ·B(k)+ . . . +H _(T)(k)·W _(T) ·B(k)+N(k),  Eq (3)

where

W_(t) is a weight for physical antenna t, where tε{1, . . . , T},

H_(t)(k) is a channel response for physical antenna t on subcarrier k,

Y(k) is a received symbol for subcarrier k, and

N(k) is noise on carrier k.

Equation (3) may be expressed in vector form, as follows:

Y(k)=H(k)·W·B(k)+N(k)=H _(eff)(k)·B(k)+N(k),  Eq (4)

where

H(k)=[H₁(k) . . . H_(T)(k)] is a row vector of channel gains, and

H_(eff)(k) is a channel gain for an effective channel on subcarrier k.

The UE may estimate the channel response for each physical antenna basedon the reference signal transmitted from that antenna. The UE may obtainĤ(k), which is an estimate of H(k), for each subcarrier k of interest.The UE may also know the weights W for the T physical antennas. The UEmay derive a channel estimate for the effective channel based on Ĥ(k)and W.

In one design, the UE may perform detection based on a minimum meansquare error (MMSE) technique, as follows:

$\begin{matrix}{{{\hat{B}(k)} = \frac{{{\hat{H}}_{eff}^{*}(k)} \cdot {Y(k)}}{{{{\hat{H}}_{eff}(k)}}^{2} + {\sigma_{n}^{2}(k)}}},} & {{Eq}\mspace{14mu} (5)}\end{matrix}$

where

Ĥ_(f) (k)=Ĥ(k)·W is an effective channel gain estimate for subcarrier k,

{circumflex over (B)}(k) is a detected symbol for subcarrier k, which isan estimate of B(k),

σ_(n) ²(k) is the variance of the noise N(k), and

“*” denotes a complex conjugate.

The UE may also perform detection based on least squares (LS) technique.In this case, the noise variance in equation (5) may be omitted. The UEmay also perform detection in other manners. The UE may then process thedetected symbols {circumflex over (B)}(k) to determine symbol X for theoverload indicator.

In another design, the UE may find symbol X that minimizes the errorbetween the actual received symbols at the UE and hypothesized receivedsymbols. When symbol X is a BPSK or QPSK modulation symbol (or moregenerally, when |X|²=1), the problem reduces to a correlation as follow:

$\begin{matrix}{{C_{i} = {\sum\limits_{k}\; {\left\lbrack {{Y(k)} - {{{\hat{H}}_{eff}(k)} \cdot X_{i} \cdot {A(k)}}} \right\rbrack^{2}/\sigma^{2}}}},} & {{Eq}\mspace{14mu} (6)}\end{matrix}$

where

σ² is residual noise power in {circumflex over (B)}(k),

X_(i) is the i-th possible value of symbol X, and

C_(i) is a correlation result for X_(i).

The UE typically knows A(k) by the time it attempts to determine theoverload indicator. For example, the UE may perform PSS/SSS detection todetect for A(k) in the same manner as a legacy UE that is unaware of thebeam used for the PSS/SSS. The UE may perform correlation as shown inequation (6) for each possible value of X. The UE may provide the valueof X_(i) that yields the smallest correlation result as the symbol thatis most likely to be transmitted.

The UE may also perform detection in other manners. For example, the UEmay perform a time or frequency correlation between the symbols for thePSS/SSS and RS with the symbol for the overload indicator, possiblyafter proper filtering. To reduce hardware complexity, the UE may usehardware components in a searcher and/or a measurement report engine atthe UE.

For the first OICH design, UEs that can receive the OICH may performdetection as described above to recover the overload indicator. UEs thatcannot receive the OICH (which may be referred to as legacy UEs) may beunaffected by the transmission of the overload indicator on both the PSSand SSS. The legacy UEs would observe an effective weight of W_(t)·X foreach physical antenna. Since the same beam is used for eachtransmission/instance of the PSS and SSS, the operation of the legacyUEs is unaffected.

In a second OICH design, an overload indicator may be transmitted as aphase difference between consecutive transmissions of the PSS/SSS for acell. The first transmission of the PSS/SSS may be used as a referencephase. The overload indicator may be transmitted by varying the phase ofthe second transmission of the PSS/SSS relative to the reference phase.The two transmissions of the PSS/SSS may be sent in subframes 0 and 5 ofthe same radio frame for LTE FDD.

For the second OICH design, the same beam may be used for a timeinterval covering at least two consecutive transmissions of the PSS/SSS.A time interval may cover one or more radio frames, and each radio framemay include two transmissions of the PSS and SSS, as shown in FIG. 2.The beam may change from time interval to time interval and may not needto be conveyed to the UEs. For the first transmission, symbols A(k) maybe mapped to the 62 subcarriers used for the PSS/SSS. For the secondtransmission, modulated symbols B(k) may be mapped to the 62 subcarriersused for the PSS/SSS.

A UE may first determine A(k), e.g., using neighbor cell searchtechniques similar to those used by legacy UEs. The UE may receive thetwo transmissions of the PSS/SSS from the cell. The UE may process thefirst transmission of the PSS/SSS and may use its knowledge of A(k) toderive channel gain estimates Ĥ_(eff)(k) for the effective channel. TheUE may process the second transmission of the PSS/SSS to recover symbolX based on the channel gain estimates, e.g., as described above for thefirst OICH design.

Since the first transmission of the PSS/SSS is used as a phase referencefor the second transmission of the PSS/SSS, the two transmissions shouldbe sent as close in time as possible. This may ensure that the channelestimates obtained based on the first transmission of the PSS/SSS are areasonably accurate estimate of the channel response during the secondtransmission of the PSS/SSS.

For the first and second OICH designs, the overload indicator istransmitted on the PSS/SSS, which is normally received by UEs. Noadditional signals and no extra overhead are needed to transmit theoverload indicator. Furthermore, transmitting the overload indicator onboth the PSS and SSS does not impact the operation of legacy UEs, whichmay consider symbol X for the overload indicator as part of the beam.For the first OICH design, the beam information may be specified in thestandard and/or may be sent infrequently over the air.

For a synchronous system, a UE may receive the PSS and SSS from allcells in the same subframe. For an asynchronous system, the UE mayreceive the PSS and SSS from each cell based on the frame timing of thatcell. The UE may operate with discontinuous reception (DRX). In thiscase, for an asynchronous system, the UE may receive the overloadindicator on only some of the PSS and SSS transmissions in order toreduce its reception time.

In a third OICH design, an overload indicator may be transmitted onresources reserved for transmitting the overload indicator. The reservedresources may comprise one or more resource blocks, a set of resourceelements, etc. The overload indicator may be intended for UEs inneighbor cells. The reserved resources may be conveyed to the UEs toenable the UEs to receive the overload indicator.

In a first resource reservation design, some resources in the dataregion (e.g., some resource elements in the data region of at least oneresource block) may be reserved for transmitting the overload indicator.No data may be transmitted on these reserved resources. For LTE, theoverload indicator may be transmitted on the PDSCH or some otherphysical channel in the data region. In a second resource reservationdesign, some resources in the control region (e.g., some resourceelements in the control region) may be reserved for transmitting theoverload indicator. No control information may be transmitted on thesereserved resources. For LTE, the overload indicator may be transmittedon reserved resources by setting aside some of the PHICH, PDCCH, and/orsome other physical channel resources in the control region for thispurpose. For both resource reservation designs, the reserved resourcesmay vary across frequency over time to obtain diversity.

In one design, the reserved resources may occupy a small number ofsubcarriers in a small bandwidth to allow UEs to use smaller inversefast Fourier transform (IFFT) to process the overload indicator fromneighbor cells. In one design, the reserved resources may occupy all ora subset of the 73 subcarriers in the center 1095 KHz of the systembandwidth, or 36 subcarriers on each side of the center/DC subcarrier.This design may allow UEs to receive the overload indicator as well as(i) the PSS and SSS transmitted in the center 945 KHz of the systembandwidth and (ii) the PBCH transmitted in the center 1095 KHz of thesystem bandwidth.

FIG. 5A shows a design of reserving resources in the data region of apair of resource blocks for transmitting an overload indicator. In thisdesign, the resource block pair is one of the six resource block pairsin which the PSS and SSS are transmitted in the center 945 KHz insubframe 5. The reserved resources may include all resource elements inthe data region that are not used for the PSS, the SSS, or the RS. Theoverload indicator may be transmitted on the reserved resources in theresource block pair. Since the PBCH is not transmitted in subframe 5,more resource elements may be available for transmitting the overloadindicator.

FIG. 5B shows another design of transmitting an overload indicator onthe reserved resources in a resource block pair. In this design, thereserved resources may include all resource elements in the data regionthat are not used for the PSS, the SSS, or the RS, as described abovefor FIG. 5A. Some of the reserved resources may be used to transmitadditional reference symbols (labeled as “A” in FIG. 5B), and theremaining reserved resources may be used to transmit the overloadindicator. FIG. 5B shows an exemplary set of resource elements used forthe additional reference symbols. Other resource elements may also beused to transmit the additional reference symbols. In any case, theadditional reference symbols may be used by UEs to derive a moreaccurate channel estimate, which may improve detection performance.

In a third resource reservation design, unused resource elements nearthe PSS and SSS and/or unused resource elements in a PBCH region may bereserved for transmitting the overload indicator. This design may allowthe overload indicator to be transmitted without consuming anyadditional resources.

FIG. 6A shows a design of reserving unused resource elements near thePSS and SSS and/or in the PBCH region for transmitting an overloadindicator for a case with one physical antenna. FIG. 6A shows three ofthe six resource block pairs used to transmit the PSS, SSS, and PBCH insubframe 0. These six resource block pairs occupy 36 subcarriers on eachside of the center/DC subcarrier, which covers the center 1095 KHz ofthe system bandwidth. The PSS and SSS are transmitted on the center 62subcarriers in symbol periods 6 and 5, respectively. Ten unused resourceelements (labeled as “U” in FIG. 6A) on both sides of the PSS and SSS insymbol periods 6 and 5 may be reserved for transmitting the overloadindicator.

The PBCH region covers the center 72 subcarriers in symbol periods 7through 10 in subframe 0. The PBCH is transmitted on resource elementswithout any label in the PBCH region in FIG. 6A. Some resource elementsin the PBCH region are used to transmit the RS from antenna 0 and arelabeled with “R” in FIG. 6A. Some resource elements in the PBCH regionare unused and are labeled with “U” in FIG. 6A. The unused resourceelements in the PBCH region may be reserved for transmitting theoverload indicator.

FIG. 6B shows a design of reserving unused resource elements near thePSS and SSS and/or in the PBCH region for transmitting an overloadindicator for a case with two physical antennas. The PSS and SSS aretransmitted on the center 62 subcarriers in symbol periods 6 and 5,respectively. Ten unused resource elements on both sides of the PSS andSSS may be reserved for transmitting the overload indicator.

The PBCH region covers the center 72 subcarriers in symbol periods 7through 10 in subframe 0. Some resource elements in the PBCH region areused to transmit the RS from two physical antennas and are labeled with“R” in FIG. 6B. Some resource elements in the PBCH region are unused andare labeled with “U” in FIG. 6B. The unused resource elements in thePBCH region may be reserved for transmitting the overload indicator.

The PBCH region does not include any unused resource elements for thecase of four physical antennas. However, the ten unused resourceelements on both sides of the PSS and SSS may be reserved fortransmitting the overload indicator.

As shown in FIGS. 6A and 6B, at least 20 unused resource elements nearthe PSS and SSS and in the PBCH region may be reserved for transmittingan overload indicator. For a synchronous system, reuse may be applied,and each cell may transmit its overload indicator on only some of theseresource elements. For both synchronous and asynchronous systems, theoverload indicator may be transmitted at a higher power level on theseresource elements to enable reliable reception by UEs in neighbor cells.Transmitting the overload indicator on the unused resource elements mayavoid impact to legacy UEs.

In general, some resources in regular subframes, or multicast/broadcastsingle frequency network (MBSFN) subframes, or blank subframes, or someother subframes may be reserved for transmitting the overload indicator.MBSFN subframes are subframes normally used to send multicast and/orbroadcast data to multiple UEs. An MBSFN subframe may have the RStransmitted in fewer symbol periods, which may allow more of thesubframe to be used for other transmissions. A blank subframe includesno mandated transmissions of RS, control information, and data. Anadvantage of using blank or MBSFN subframes for the overload indicatoris that these subframes include fewer or no reference signals, so that aUE attempting to receive the overload indicator from a neighbor cell mayobserve less interference from its serving cell and other neighborcells. For example, the serving cell may blank the portion where UEs areexpected to receive the overload indicators from neighbor cells or whentime and/or frequency reuse is employed. The reserved resources may bestatic and not changed, or semi-static and changed slowly, or dynamicand changed as often as necessary.

The reserved resources for the overload indicator may be conveyed to theUEs in various manners. For example, the reserved resources may beconveyed via the PSS, the SSS, the PBCH, and/or other signals andchannels. In one design, a cell may convey its reserved resources (whichmay be used by the cell to transmit its overload indicator) to UEs inneighbor cells via the PSS and/or the SSS (which may have widercoverage) or via the PBCH (which may have smaller coverage). In anotherdesign, a cell may convey reserved resources for neighbor cells (whichmay be used by the neighbor cells to transmit their overload indicators)to UEs served by the cell via the PSS, the SSS, the PBCH, etc. Ingeneral, a UE may be able to determine resources reserved by theneighbor cells to transmit their overload indicators based on anysuitable signal or channel transmitted by the neighbor cells and/or theserving cell.

A cell may transmit an overload indicator on the reserved resources invarious manners. In one design, the overload indicator may be mapped toa pseudo-random sequence among a set of possible pseudo-randomsequences. The pseudo-random sequence may then be mapped to the reservedresources. In another design, the overload indicator may be encoded andsymbol mapped to a set of symbols, where each symbol may be a real orcomplex value. The symbols may be mapped to the reserved resources.

In one design, the overload indicator may be transmitted with precodingusing the same beam used for the PSS and SSS. This design may allow a UEto use the PSS/SSS as a phase reference for detecting the overloadindicator. The use of the PSS/SSS (instead of the RS) as a phasereference for the overload indicator may allow the UE to obtain a singlechannel estimate for the effective channel even if the cell has morethan one physical antenna. This may minimize channel estimation losses,which may be especially severe at low received signal quality. Theadditional reference symbols (e.g., as shown in FIG. 5B) may furtherimprove channel estimation performance, which may then improve detectionperformance. In another design, the overload indicator may betransmitted without precoding. For this design, a UE may derive achannel estimate based on the RS (instead of the PSS/SSS). In yetanother design, the overload indicator may be transmitted with precodingfor a beam that is known to the UEs but may be different from a beamused for the PSS and SSS. This design may allow a cell to independentlycontrol the beam for the PSS and SSS and the beam for the overloadindicator. A UE may derive a channel estimate based on the RS and theknown beam for the overload indicator. For all designs, the additionalreference symbols may be transmitted in the same manner as the overloadindicator (e.g., with or without precoding).

A cell may transmit an overload indicator on the reserved resources in amanner to allow the UEs to recover the overload indicator from the cell.If multiple cells can transmit their overload indicators on the sameresources, then each cell may transmit its overload indicator such thatthe UEs can identify the sender of the overload indicator. For example,each cell may scramble its overload indicator with a scrambling sequenceassigned to the cell, e.g., a scrambling sequence generated based on thecell ID. In this case, the UEs may determine the cell ID of a cell priorto receiving the overload indicator from the cell. The cell ID may beobtained from the PSS and SSS transmitted by the cell, from a neighborcell list transmitted by the serving cell, or from other sources.

A cell may transmit its overload indicator on the reserved resources atany suitable rate. If the overload indicator is transmitted at asufficiently fast rate (e.g., in every subframe), then a UE may operatewith DRX and may receive the overload indicator only some of the time(instead of each transmission of the overload indicator). The cell mayalso transmit the overload indicator at higher transmit power relativeto the transmit power for data (i.e., with power boosting) to achievedeeper penetration in neighbor cells. The cell may also transmit theoverload indicator on the reserved resources in addition to transmittingthe overload indicator on the PSS/SSS. Thus, the third OICH design maybe used in combination with the first or second OICH design.

In a fourth OICH design, an overload indicator may be transmitted on alow reuse channel that may observe less interference from neighborcells. Some resources may be reserved for the low reuse channel. Eachcell may transmit its low reuse channel on some of the reservedresources. The low reuse channel may carry the overload indicator andpossibly other information such as cell ID, master information block(MIB), etc.

The low reuse channel may be transmitted with a reuse factor greaterthan one, so that only a fraction of the cells transmit their low reusechannels on a given resource. For example, with a reuse factor of M,where M>1, only one out of every M cells may transmit its low reusechannel on a given resource. The low reuse channel from a given cell mayobserve less interference from other cells, which may enable receptionof the low reuse channel by more UEs. Transmissions on the low reusechannel may also be randomized in order to avoid situations wheretransmissions from a strong interfering cell always collide withtransmissions from a weaker desired cell.

In one design, the low reuse channel may comprise a low reusepreamble/pilot (LRP), which may have wider coverage and betterhearability than the RS. An LRP may also be referred to as a positioningassistance reference signal (PA-RS), a highly detectable pilot (HDP),etc. The overload indicator may be mapped to one or more symbols, whichmay be sent on the LRP. For example, the overload indicator may bemapped to a single symbol, which may be used to modulate each symbol forthe LRP, e.g., as shown in equation (1).

In another design, the low reuse channel carrying the overload indicatormay be transmitted on guard subcarriers. A total of N_(FFT) subcarriersmay be obtained from OFDM or SC-FDM, but only a subset of these N_(FFT)subcarriers may be used for transmission. The remaining subcarriers,which may be located near the two edges of the system bandwidth, may beleft unused and may serve as guard subcarriers to allow the system tomeet spectral emission requirements. Some or all of the guardsubcarriers may be used for the low reuse channel. Random reuse may beemployed, and each cell may randomly select a set of subcarriers totransmit its low reuse channel.

In a variation of the fourth OICH design, an overload indicator may betransmitted on the PBCH. This may be achieved in several manners. In afirst PBCH design, a cell may transmit its overload indicator on itsPBCH to UEs in neighbor cells. For this design, a UE may process thePBCHs of neighbor cells to obtain the overload indicators for thesecells. The UE may then control its operation and/or perform otheractions based on the overload indicators for the neighbor cells. Thisdesign may provide good processing gain but lower coverage due totransmission of the overload indicator on the PBCH. Furthermore, theperiodicity of the overload indicator would be dependent on theperiodicity of the PBCH, which is 40 ms for LTE.

In a second PBCH design, a cell may transmit overload indicators forneighbor cells on the PBCH of the cell. The cell may receive theoverload indicators for the neighbor cells, e.g., via the backhaul. Thecell may transmit these overload indicators on the PBCH to its UEs. ThePBCH may be defined with one or more fields to carry one or moreoverload indicators for one or more neighbor cells. The UEs within thecoverage of the cell may process the PBCH of the cell to obtain theoverload indicators for the neighbor cells. These UEs may then controltheir operation and/or perform other actions based on the overloadindicators for the neighbor cells.

For the first PBCH design, a UE may receive the PBCHs of neighbor cellsin order to obtain the overload indicators for these cells. The PBCHfrom each cell may be intended for UEs in that cell and possibly strongUEs in neighbor cells and may thus have limited penetration. The UE mayprocess the PBCHs for the neighbor cells using interference cancellationin order to improve detection performance. For interferencecancellation, the UE may process a received signal to recover the PBCHfor one (e.g., the strongest) neighbor cell at a time. Upon correctlydecoding the PBCH for one neighbor cell, the UE may estimate theinterference due to the PBCH, subtract the estimated interference fromthe received signal, and process the interference-canceled signal torecover the PBCH for another neighbor cell.

Various designs for transmitting an overload indicator have beendescribed above. The overload indicator may also be transmitted in othermanners. The overload indicator may be transmitted in a manner to avoidor minimize changes to existing signals and channels in LTE Release 8.The overload indicator may also be transmitted in a manner to allow UEsto receive the overload indicators from (i) synchronous and asynchronouscells and (ii) very weak neighbor cells with low received signalquality. For example, the overload indicator may have penetrationsimilar to (or better than) that of the PSS and SSS. The overloadindicator may also be transmitted at a suitable periodicity (e.g., inthe range of 5 to 30 ms), which may be selected to achieve a goodcompromise between performance (which may favor higher periodicity) andoverhead (which may favor lower periodicity). The overload indicator maybe transmitted in each radio frame for a periodicity of 10 ms. Theoverload indicators for different cells may be transmitted attime-frequency locations that may vary from time to time to avoidrepeated collisions of the overload indicators from these cells at theUEs.

An overload indicator may also be transmitted in a manner to imposeminimal additional complexity on a UE for detection of the overloadindicator. This may be achieved by transmitting the overload indicatorusing existing signals (e.g., the SSS). This may also be achieved bytransmitting the overload indicator in the center six resource blockpairs, which may already be monitored by the UEs for detecting new cellsand tracking detected cells.

An overload indicator may be transmitted in a manner such that detectionof the overload indicator has as little impact as possible on batterylife of UEs operating with DRX. This may be achieved by transmitting theoverload indicator in subframe 0 and/or 5, since the UEs may already bemonitoring these subframes for cell detection and tracking. Since thePBCH is transmitted in subframe 0 and not subframe 5, subframe 5 mayhave more resource elements that may be used for the overload indicator.The periodicity of the overload indicator may be larger than or equal to20 ms to avoid transmissions of system information block 1 (SIB 1) insubframe 5.

The system may support operation on multiple carriers, and each carriermay be defined by a specific frequency range and a specific centerfrequency. In one design, an overload indicator may be transmitted by acell on a given downlink carrier and may control transmission of UEs onone or more uplink carriers. In another design, multiple overloadindicators covering different uplink carriers may be transmitted on thesame or different downlink carriers. When multiple overload indicatorsare transmitted on one downlink carrier, the overload indicators may betransmitted on different resources (e.g., different resource blocks). Anoverload indicator may also be used to control interference caused byAdjacent Carrier Leakage Ratio (ACLR), which may result when a UEtransmitting on one carrier causes interference on an adjacent carrier.The same overload indicator or different overload indicators may be usedto control co-channel interference and ACLR.

A UE in DRX may monitor only a subset of all transmissions of anoverload indicator in order to reduce impact on battery life. The UE inDRX may also ignore all transmissions of the overload indicator, e.g.,if the UE is not allowed to transmit on the uplink in the DRX mode. Inthis case, the serving cell may assign a conservative initial transmitpower level (e.g., based on open loop projection) for any uplinktransmission that occurs after a long DRX cycle.

A UE may monitor overload indicators from multiple neighbor cells withsimilar (but possibly asynchronous) timing. The UE may receive only someof the transmissions of the overload indicators from different cells viasubsampling. The UE may control its transmission to account forsubsampling. For example, the UE may adjust its transmit power by applyadditional step sizes to account for missed overload indicators due tosubsampling.

FIG. 7 shows a design of a process 700 for transmitting an overloadindicator based on the first OICH design. Process 700 may be performedby a cell (e.g., a base station/eNB for the cell) or by some otherentity. The cell may determine an overload indicator based on itsloading (block 712). The cell may transmit a reference signal that maybe used by UEs for channel estimation and/or other purposes (block 714).The cell may transmit at least one synchronization signal comprising theoverload indicator for the cell (block 716). The at least onesynchronization signal may be used by the UEs for cell acquisitionand/or other purposes and may comprise a primary synchronization signaland/or a secondary synchronization signal. The overload indicator may betransmitted on the at least one synchronization signal, and thereference signal may be used as a phase reference.

In one design, the at least one synchronization signal may betransmitted with precoding along a beam, and the reference signal may betransmitted without precoding. The cell may transmit informationindicative of the precoding or beam used for the at least onesynchronization signal. Alternatively, the precoding or beam may bespecified and known a priori by the UEs.

In one design, the cell may generate a plurality of symbols for asynchronization signal among the at least one synchronization signal.The cell may generate a symbol for the overload indicator. The cell maymultiply the plurality of symbols for the synchronization signal withthe symbol for the overload indicator to obtain a plurality of modulatedsymbols, e.g., as shown in equation (1). The cell may then generate thesynchronization signal based on the plurality of modulated symbols(instead of the plurality of symbols).

In one design, the overload indicator may comprise at least one bitindicative of the loading of the cell. For example, the overloadindicator may indicate whether the cell observes heavy loading. Theoverload indicator may be transmitted on a downlink carrier and mayindicate loading of at least one uplink carrier associated with thedownlink carrier.

FIG. 8 shows a design of an apparatus 800 for transmitting an overloadindicator. Apparatus 800 includes a module 812 to determine an overloadindicator for a cell, a module 814 to transmit a reference signal forthe cell, and a module 816 to transmit at least one synchronizationsignal comprising the overload indicator for the cell. The overloadindicator may be transmitted on the at least one synchronization signal,and the reference signal may be used as a phase reference.

FIG. 9 shows a design of a process 900 for transmitting an overloadindicator based on the second OICH design. Process 900 may be performedby a cell or by some other entity. The cell may determine an overloadindicator based on its loading (block 912). The cell may send a firsttransmission of at least one synchronization signal (e.g., the PSSand/or SSS) in a first time period (block 914). The cell may send asecond transmission of the at least one synchronization signalcomprising the overload indicator in a second time period (block 916).The overload indicator may be conveyed by a phase difference between thesecond transmission and the first transmission of the at least onesynchronization signal. In one design, for LTE, the first time periodmay correspond to subframe 0 of a radio frame, and the second timeperiod may correspond to subframe 5 of the radio frame.

In one design, the cell may generate a plurality of symbols for asynchronization signal among the at least one synchronization signal.The cell may generate a symbol for the overload indicator. The cell maymultiply the plurality of symbols for the synchronization signal withthe symbol for the overload indicator to obtain a plurality of modulatedsymbols. The cell may generate the first transmission of thesynchronization signal based on the plurality of symbols. The cell maygenerate the second transmission of the synchronization signal based onthe plurality of modulated symbols. The cell may send the first andsecond transmissions of the at least one synchronization signal withprecoding for a beam that may be used for both transmissions.

FIG. 10 shows a design of an apparatus 1000 for transmitting an overloadindicator. Apparatus 1000 includes a module 1012 to determine anoverload indicator for a cell, a module 1014 to send a firsttransmission of at least one synchronization signal for the cell in afirst time period, and a module 1016 to send a second transmission ofthe at least one synchronization signal comprising the overloadindicator in a second time period. The overload indicator may beconveyed by a phase difference between the second transmission and thefirst transmission of the at least one synchronization signal.

FIG. 11 shows a design of a process 1100 for transmitting an overloadindicator based on the third OICH design. Process 1100 may be performedby a cell or by some other entity. The cell may determine an overloadindicator based on its loading (block 1112). The cell may determineresources reserved for transmitting the overload indicator (block 1114).In one design, the reserved resources comprise resource elements in adata region of at least one resource block. In another design, thereserved resources may comprise resource elements in a control region ofat least one resource block. In yet another design, the reservedresources may comprise unused resource elements in at least one resourceblock. For all designs, the cell may transmit the overload indicator onthe reserved resources to UEs in neighbor cells (block 1116).

The cell may transmit at least one synchronization signal in a centerportion of the system bandwidth. The reserved resources may compriseresource elements in the center portion of the system bandwidth, whichmay simplify reception of the overload indicator by the UEs. The cellmay transmit the at least one synchronization signal in designatedsubframes (e.g., subframes 0 and 5) among available subframes. Thereserved resources may comprise resource elements in all or a subset ofthe designated subframes, which may reduce reception time for the UEssince they may normally receive the at least one synchronization signal.The cell may transmit the at least one synchronization signal in atleast one symbol period. The reserved resources comprise unused resourceelements in the at least one symbol period.

The cell may transmit a broadcast channel on a first set of resourceelements in a broadcast region (e.g., the PBCH region) and may transmita reference signal on a second set of resource elements in the broadcastregion. The broadcast region may cover a plurality of subcarriers in aplurality of symbol periods. The reserved resources may compriseresource elements in the broadcast region that are not used for thebroadcast channel or the reference signal.

In one design, the cell may transmit the at least one synchronizationsignal with precoding and may also transmit the overload indicator withprecoding. The at least one synchronization signal may provide a phasereference for the overload indicator. In another design, the cell maytransmit the overload indicator without precoding. The cell may transmita reference signal that may provide a phase reference for the overloadindicator. The cell may also transmit an additional reference signal.

FIG. 12 shows a design of an apparatus 1200 for transmitting an overloadindicator. Apparatus 1200 includes a module 1212 to determine anoverload indicator for a cell, a module 1214 to determine resourcesreserved for transmitting the overload indicator, and a module 1216 totransmit the overload indicator for the cell on the reserved resourcesto UEs in neighbor cells.

FIG. 13 shows a design of a process 1300 for transmitting an overloadindicator based on the fourth OICH design. Process 1300 may be performedby a cell or by some other entity. The cell may determine an overloadindicator based on its loading (block 1312). The cell may transmit theoverload indicator on a low reuse channel or a broadcast channel to UEsin neighbor cells (block 1314). The cell may also obtain at least oneoverload indicator for at least one neighbor cell and may transmit theat least one overload indicator on the low reuse channel or thebroadcast channel.

The low reuse channel may be transmitted with a reuse factor greaterthan one, so that only a fraction of the cells transmit their low reusechannels on a given resource and hence cause less interference. In onedesign, the low reuse channel may comprise a low reuse preamble that maybe transmitted with a reuse factor greater than one. In another design,the low reuse channel may be transmitted on reserved resources with lowreuse. The reserved resources may occupy guard subcarriers, which maynot be used for transmission of data and control information. The cellmay randomly select some of the reserved resources for transmitting thelow reuse channel and may transmit the low reuse channel on the selectedresources.

FIG. 14 shows a design of an apparatus 1400 for transmitting an overloadindicator. Apparatus 1400 includes a module 1412 to determine anoverload indicator for a cell, and a module 1414 to transmit theoverload indicator for the cell on a low reuse channel or a broadcastchannel to UEs in neighbor cells.

FIG. 15 shows a design of a process 1500 for receiving overloadindicators transmitted based on the first OICH design. Process 1500 maybe performed by a UE (as described below) or by some other entity. TheUE may communicate with a serving cell. The UE may receive a referencesignal from a neighbor cell (block 1512). The UE may also receive atleast one synchronization signal (e.g., the PSS and/or SSS) from theneighbor cell (block 1514). The at least one synchronization signal maycomprise an overload indicator for the neighbor cell.

The UE may perform detection for the at least one synchronization signalbased on the reference signal to recover the overload indicator for theneighbor cell (block 1516). In one design, the UE may derive a channelestimate for the neighbor cell based on the reference signal. The UE maythen perform detection for the at least one synchronization signal basedon the channel estimate to recover the overload indicator for theneighbor cell. The at least one synchronization signal may betransmitted with precoding, and the reference signal may be transmittedwithout precoding. In this case, the UE may derive an effective channelestimate for the neighbor cell based on the channel estimate and theweights for the precoding. The UE may then perform detection for the atleast one synchronization signal based on the effective channelestimate, e.g., as shown in equation (5) or (6).

The UE may determine loading of the neighbor cell based on the overloadindicator (block 1518). The UE may control its operation based on theloading of the neighbor cell (block 1520). For example, the UE mayadjust its transmit power, or skip one or more transmissions, or avoidtransmitting on one or more resources, and/or perform other actionsbased on the loading of the neighbor cell. Alternatively oradditionally, the UE may determine feedback information based on theoverload indicator for the neighbor cell. The UE may send the feedbackinformation to the serving cell, which may perform appropriatecorrective actions.

FIG. 16 shows a design of an apparatus 1600 for receiving overloadindicators. Apparatus 1600 includes a module 1612 to receive a referencesignal from a neighbor cell at a UE, a module 1614 to receive at leastone synchronization signal from the neighbor cell at the UE, with the atleast one synchronization signal comprising an overload indicator forthe neighbor cell, a module 1616 to perform detection for the at leastone synchronization signal based on the reference signal to recover theoverload indicator for the neighbor cell, a module 1618 to determineloading of the neighbor cell based on the overload indicator, and amodule 1620 to control operation of the UE based on the loading of theneighbor cell.

FIG. 17 shows a design of a process 1700 for receiving overloadindicators transmitted based on the second OICH design. Process 1700 maybe performed by a UE or by some other entity. The UE may receive a firsttransmission of at least one synchronization signal (e.g., the PSSand/or SSS) from a neighbor cell in a first time period (block 1712).The UE may receive a second transmission of the at least onesynchronization signal from the neighbor cell in a second time period(block 1714). The second transmission of the at least onesynchronization signal may comprise an overload indicator for theneighbor cell. The UE may perform detection for the second transmissionof the at least one synchronization signal based on the firsttransmission of the at least one synchronization signal to recover theoverload indicator for the neighbor cell (block 1716). For example, theUE may derive a channel estimate for the neighbor cell based on thefirst transmission of the at least one synchronization signal. The UEmay then perform detection for the second transmission of the at leastone synchronization signal based on the channel estimate to recover theoverload indicator for the neighbor cell.

The UE may determine loading of the neighbor cell based on the overloadindicator and may control its operation based on the loading of theneighbor cell. The UE may also determine feedback information based onthe overload indicator and may send the feedback information to theserving cell.

FIG. 18 shows a design of an apparatus 1800 for receiving overloadindicators. Apparatus 1800 includes a module 1812 to receive a firsttransmission of at least one synchronization signal from a neighbor cellin a first time period at a UE, a module 1814 to receive a secondtransmission of the at least one synchronization signal from theneighbor cell in a second time period at the UE, the second transmissionof the at least one synchronization signal comprising an overloadindicator for the neighbor cell, and a module 1816 to perform detectionfor the second transmission of the at least one synchronization signalbased on the first transmission of the at least one synchronizationsignal to recover the overload indicator for the neighbor cell.

FIG. 19 shows a design of a process 1900 for receiving overloadindicators transmitted based on the third OICH design. Process 1900 maybe performed by a UE or by some other entity. The UE may determineresources reserved for transmitting an overload indicator for a neighborcell (block 1912). The reserved resources may comprise (i) resourceelements in a data region of at least one resource block, (ii) resourceelements in a control region of at least one resource block, (iii)unused resource elements in at least one resource block, and/or (iv)other resource elements. The UE may receive the overload indicator forthe neighbor cell on the reserved resources (block 1914). The UE mayreceive each transmission of the overload indicator for the neighborcell or may receive only a subset of all transmissions of the overloadindicator in order to reduce reception time for the UE.

In one design that is shown in FIG. 19, the UE may receive at least onesynchronization signal transmitted by the neighbor cell with precoding(block 1916). The overload indicator may also be transmitted by theneighbor cell with precoding. The UE may derive a channel estimate forthe neighbor cell based on the at least one synchronization signal(block 1918). The UE may then perform detection based on the channelestimate to recover the overload indicator for the neighbor cell (block1920).

In another design that is not shown in FIG. 19, the UE may receive areference signal and possibly an additional reference signal from theneighbor cell. The UE may derive a channel estimate for the neighborcell based on the reference signal(s). The UE may then perform detectionbased on the channel estimate to recover the overload indicator for theneighbor cell. The overload indicator may or may not be transmitted bythe neighbor cell with precoding. If the overload indicator istransmitted with precoding, then the UE may derive an effective channelestimate based on the channel estimate and the weights for theprecoding. The UE may then perform detection with the effective channelestimate, e.g., as shown in equation (5) or (6).

The UE may determine loading of the neighbor cell based on the overloadindicator and may control its operation based on the loading of theneighbor cell. The UE may also determine feedback information based onthe overload indicator and may send the feedback information to theserving cell.

FIG. 20 shows a design of an apparatus 2000 for receiving overloadindicators. Apparatus 2000 includes a module 2012 to determine resourcesreserved for transmitting an overload indicator for a neighbor cell, amodule 2014 to receive the overload indicator for the neighbor cell onthe reserved resources at a UE, a module 2016 to receive at least onesynchronization signal transmitted by the neighbor cell with precoding,wherein the overload indicator is transmitted by the neighbor cell withprecoding, a module 2018 to derive a channel estimate for the neighborcell based on the at least one synchronization signal, and a module 2020to perform detection based on the channel estimate to recover theoverload indicator for the neighbor cell.

FIG. 21 shows a design of a process 2100 for receiving overloadindicators transmitted based on the fourth OICH design. Process 2100 maybe performed by a UE or by some other entity. The UE may receive a lowreuse channel or a broadcast channel from a neighbor cell (block 2112).The UE may process the low reuse channel or the broadcast channel torecover an overload indicator for the neighbor cell (block 2114). Thelow reuse channel may be transmitted with a reuse factor greater thanone and may observe less interference from other cells. The low reusechannel may comprise a low reuse preamble or may be sent on reservedresources (e.g., guard subcarriers) with low reuse.

The UE may determine loading of the neighbor cell based on the overloadindicator and may control its operation based on the loading of theneighbor cell. The UE may also determine feedback information based onthe overload indicator and may send the feedback information to theserving cell.

FIG. 22 shows a design of an apparatus 2200 for receiving overloadindicators. Apparatus 2200 includes a module 2212 to receive a low reusechannel or a broadcast channel from a neighbor cell at a UE, and amodule 2214 to process the low reuse channel or the broadcast channel torecover an overload indicator for the neighbor cell.

The modules in FIGS. 8, 10, 12, 14, 16, 18, 20 and 22 may compriseprocessors, electronic devices, hardware devices, electronic components,logical circuits, memories, software codes, firmware codes, etc., or anycombination thereof.

FIG. 23 shows a block diagram of a design of a UE 120 and two basestations/eNBs 110 x and 110 y, which may be one of the UEs and two ofthe base stations/eNBs in FIG. 1. Each base station may be equipped withT antennas, where T≧1, and UE 120 may be equipped with R antennas, whereR≧1. Each base station may serve one or more cells. Base station 110 xmay include a serving cell for UE 120, and base station 110 y mayinclude one or more neighbor cells for UE 120.

At each base station 110, a transmit processor 2320 may receive data forone or more UEs from a data source 2312, process (e.g., encode andmodulate) the data for each UE based on one or more modulation andcoding schemes, and provide data symbols for all UEs. Transmit processor2320 may also receive control information from a controller/processor2340, process the control information, and provide control symbols. Thecontrol information may comprise an overload indicator for each cellserved by base station 110. Transmit processor 2320 may also generatereference symbols for reference signals and synchronization signals foreach cell served by base station 110. A transmit (TX) multiple-inputmultiple-output (MIMO) processor 2330 may perform spatial processing(e.g., precoding or beamforming) on the data symbols, the controlsymbols, and/or the reference symbols, if applicable, and may provide Toutput symbol streams to T transmitters (TMTR) 2332 a through 2332 t.Each transmitter 2332 may process a respective output symbol stream(e.g., for OFDM, etc.) to obtain an output sample stream. Eachtransmitter 2332 may further process (e.g., convert to analog, amplify,filter, and upconvert) the output sample stream to obtain a downlinksignal. T downlink signals from transmitters 2332 a through 2332 t maybe transmitted via T antennas 2334 a through 2334 t, respectively.

At UE 120, R antennas 2352 a through 2352 r may receive the downlinksignals from serving base station 110 x, neighbor base station 110 y,and possibly other base stations and may provide received signals toreceivers (RCVR) 2354 a through 2354 r, respectively. Each receiver 2354may condition (e.g., filter, amplify, downconvert, and digitize) itsreceived signal to obtain received samples and may further process thereceived samples (e.g., for OFDM, etc.) to obtain received symbols. AMIMO detector 2360 may perform detection on the received symbols fromall R receivers 2354 a through 2354 r based on a channel estimate from achannel processor 2394 and may provide detected symbols. Channelprocessor 2394 may derive the channel estimate based on the referencesignals and/or the synchronization signals. A receive processor 2370 mayprocess (e.g., symbol demap and decode) the detected symbols, providedecoded data for UE 120 to a data sink 2372, and provide decoded controlinformation (e.g., overload indicators for neighbor cells) to acontroller/processor 2390. Processor 2390 may control the operation ofUE 120 based on the overload indicators for neighbor cells, e.g., asdescribed above.

On the uplink, at UE 120, data from a data source 2378 and controlinformation from controller/processor 2390 may be processed by atransmit processor 2380, precoded by a TX MIMO processor 2382 (ifapplicable), conditioned by transmitters 2354 a through 2354 r, andtransmitted via antennas 2352 a through 2352 r. At base station 110, theuplink signals from UE 120 and other UEs may be received by antennas2334, conditioned by receivers 2332, detected by a MIMO detector 2336,and processed by a receive processor 2338 to obtain the data and controlinformation transmitted by UE 120 and other UEs.

Controllers/processors 2340 x, 2340 y, and 2390 may direct the operationat base stations 110 x and 110 y and UE 120, respectively. Processor2340 and/or other processors and modules at each base station 110 mayperform or direct process 700 in FIG. 7, process 900 in FIG. 9, process1100 in FIG. 11, process 1300 in FIG. 13, and/or other processes for thetechniques described herein. Processor 2390 and/or other processors andmodules at UE 120 may perform or direct process 1500 in FIG. 15, process1700 in FIG. 17, process 1900 in FIG. 19, process 2100 in FIG. 21,and/or other processes for the techniques described herein. Memories2342 x, 2342 y and 2392 may store data and program codes for basestations 110 x and 110 y and UE 120, respectively. A scheduler 2344 ateach base station 110 may schedule UEs for transmission on the downlinkand/or uplink and may assign resources to the scheduled UEs.

Those of skill in the art would understand that information and signalsmay be represented using any of a variety of different technologies andtechniques. For example, data, instructions, commands, information,signals, bits, symbols, and chips that may be referenced throughout theabove description may be represented by voltages, currents,electromagnetic waves, magnetic fields or particles, optical fields orparticles, or any combination thereof.

Those of skill would further appreciate that the various illustrativelogical blocks, modules, circuits, and algorithm steps described inconnection with the disclosure herein may be implemented as electronichardware, computer software, or combinations of both. To clearlyillustrate this interchangeability of hardware and software, variousillustrative components, blocks, modules, circuits, and steps have beendescribed above generally in terms of their functionality. Whether suchfunctionality is implemented as hardware or software depends upon theparticular application and design constraints imposed on the overallsystem. Skilled artisans may implement the described functionality invarying ways for each particular application, but such implementationdecisions should not be interpreted as causing a departure from thescope of the present disclosure.

The various illustrative logical blocks, modules, and circuits describedin connection with the disclosure herein may be implemented or performedwith a general-purpose processor, a digital signal processor (DSP), anapplication specific integrated circuit (ASIC), a field programmablegate array (FPGA) or other programmable logic device, discrete gate ortransistor logic, discrete hardware components, or any combinationthereof designed to perform the functions described herein. Ageneral-purpose processor may be a microprocessor, but in thealternative, the processor may be any conventional processor,controller, microcontroller, or state machine. A processor may also beimplemented as a combination of computing devices, e.g., a combinationof a DSP and a microprocessor, a plurality of microprocessors, one ormore microprocessors in conjunction with a DSP core, or any other suchconfiguration.

The steps of a method or algorithm described in connection with thedisclosure herein may be embodied directly in hardware, in a softwaremodule executed by a processor, or in a combination of the two. Asoftware module may reside in RAM memory, flash memory, ROM memory,EPROM memory, EEPROM memory, registers, hard disk, a removable disk, aCD-ROM, or any other form of storage medium known in the art. Anexemplary storage medium is coupled to the processor such that theprocessor can read information from, and write information to, thestorage medium. In the alternative, the storage medium may be integralto the processor. The processor and the storage medium may reside in anASIC. The ASIC may reside in a user terminal. In the alternative, theprocessor and the storage medium may reside as discrete components in auser terminal.

In one or more exemplary designs, the functions described may beimplemented in hardware, software, firmware, or any combination thereof.If implemented in software, the functions may be stored on ortransmitted over as one or more instructions or code on acomputer-readable medium. Computer-readable media includes both computerstorage media and communication media including any medium thatfacilitates transfer of a computer program from one place to another. Astorage media may be any available media that can be accessed by ageneral purpose or special purpose computer. By way of example, and notlimitation, such computer-readable media can comprise RAM, ROM, EEPROM,CD-ROM or other optical disk storage, magnetic disk storage or othermagnetic storage devices, or any other medium that can be used to carryor store desired program code means in the form of instructions or datastructures and that can be accessed by a general-purpose orspecial-purpose computer, or a general-purpose or special-purposeprocessor. Also, any connection is properly termed a computer-readablemedium. For example, if the software is transmitted from a website,server, or other remote source using a coaxial cable, fiber optic cable,twisted pair, digital subscriber line (DSL), or wireless technologiessuch as infrared, radio, and microwave, then the coaxial cable, fiberoptic cable, twisted pair, DSL, or wireless technologies such asinfrared, radio, and microwave are included in the definition of medium.Disk and disc, as used herein, includes compact disc (CD), laser disc,optical disc, digital versatile disc (DVD), floppy disk and blu-ray discwhere disks usually reproduce data magnetically, while discs reproducedata optically with lasers. Combinations of the above should also beincluded within the scope of computer-readable media.

The previous description of the disclosure is provided to enable anyperson skilled in the art to make or use the disclosure. Variousmodifications to the disclosure will be readily apparent to thoseskilled in the art, and the generic principles defined herein may beapplied to other variations without departing from the spirit or scopeof the disclosure. Thus, the disclosure is not intended to be limited tothe examples and designs described herein but is to be accorded thewidest scope consistent with the principles and novel features disclosedherein.

What is claimed is:
 1. A method for wireless communication, comprising:determining an overload indicator for a cell; determining resourcesreserved for transmitting the overload indicator; and transmitting theoverload indicator for the cell on the reserved resources to userequipments (UEs) in neighbor cells.
 2. The method of claim 1, whereinthe reserved resources comprise resource elements in a data region of atleast one resource block.
 3. The method of claim 1, wherein the reservedresources comprise resource elements in a control region of at least oneresource block.
 4. The method of claim 1, further comprising:transmitting at least one synchronization signal in a center portion ofsystem bandwidth, and wherein the reserved resources comprise resourceelements in the center portion of the system bandwidth.
 5. The method ofclaim 1, further comprising: transmitting at least one synchronizationsignal in designated subframes among available subframes, and whereinthe reserved resources comprise resource elements in all or a subset ofthe designated subframes.
 6. The method of claim 1, further comprising:transmitting at least one synchronization signal in a center portion ofsystem bandwidth in at least one symbol period, and wherein the reservedresources comprise a plurality of resource elements not used for the atleast one synchronization signal the center portion of the systembandwidth in the at least one symbol period.
 7. The method of claim 1,further comprising: transmitting a broadcast channel on a first set ofresource elements in a broadcast region covering a plurality ofsubcarriers in a plurality of symbol periods; and transmitting areference signal on a second set of resource elements in the broadcastregion, and wherein the reserved resources comprise resource elements inthe broadcast region not used for the broadcast channel or the referencesignal.
 8. The method of claim 1, further comprising: transmitting atleast one synchronization signal with precoding, wherein the overloadindicator is transmitted with precoding, and wherein the at least onesynchronization signal provides a phase reference for the overloadindicator.
 9. The method of claim 1, further comprising: transmitting areference signal for the cell, and wherein the reference signal providesa phase reference for the overload indicator.
 10. An apparatus forwireless communication, comprising: means for determining an overloadindicator for a cell; means for determining resources reserved fortransmitting the overload indicator; and means for transmitting theoverload indicator for the cell on the reserved resources to userequipments (UEs) in neighbor cells.
 11. The apparatus of claim 10,wherein the reserved resources comprise resource elements in a dataregion or a control region of at least one resource block.
 12. Theapparatus of claim 10, further comprising: means for transmitting atleast one synchronization signal in a center portion of systembandwidth, and wherein the reserved resources comprise resource elementsin the center portion of the system bandwidth.
 13. The apparatus ofclaim 10, further comprising: means for transmitting at least onesynchronization signal in designated subframes among availablesubframes, and wherein the reserved resources comprise resource elementsin all or a subset of the designated subframes.
 14. A method forwireless communication, comprising: determining an overload indicatorfor a cell; and transmitting the overload indicator for the cell on alow reuse channel or a broadcast channel to user equipments (UEs) inneighbor cells.
 15. The method of claim 14, wherein the low reusechannel comprises a low reuse preamble transmitted with a reuse factorgreater than one.
 16. The method of claim 14, further comprising:determining resources reserved for the low reuse channel, and whereinthe reserved resources for the low reuse channel occupy guardsubcarriers not used for transmission of data and control information.17. The method of claim 14, further comprising: determining resourcesreserved for the low reuse channel; and randomly selecting some of thereserved resources for transmitting the low reuse channel, and whereinthe low reuse channel is transmitted on the selected resources.
 18. Themethod of claim 14, further comprising: obtaining at least one overloadindicator for at least one neighbor cell; and transmitting the at leastone overload indicator for the at least one neighbor cell on thebroadcast channel.
 19. An apparatus for wireless communication,comprising: means for determining an overload indicator for a cell; andmeans for transmitting the overload indicator for the cell on a lowreuse channel or a broadcast channel to user equipments (UEs) inneighbor cells.
 20. The apparatus of claim 19, further comprising: meansfor determining resources reserved for the low reuse channel, andwherein the reserved resources for the low reuse channel occupy guardsubcarriers not used for transmission of data and control information.21. The apparatus of claim 19, further comprising: means for determiningresources reserved for the low reuse channel; and means for randomlyselecting some of the reserved resources for transmitting the low reusechannel, and wherein the low reuse channel is transmitted on theselected resources.
 22. A method for wireless communication, comprising:receiving a reference signal from a neighbor cell at a user equipment(UE); and receiving at least one synchronization signal from theneighbor cell at the UE, the at least one synchronization signalcomprising an overload indicator for the neighbor cell.
 23. The methodof claim 22, further comprising: deriving a channel estimate for theneighbor cell based on the reference signal; and performing detectionfor the at least one synchronization signal based on the channelestimate to recover the overload indicator for the neighbor cell. 24.The method of claim 22, wherein the at least one synchronization signalis transmitted with precoding and the reference signal is transmittedwithout precoding, the method further comprising: deriving a channelestimate for the neighbor cell based on the reference signal; derivingan effective channel estimate for the neighbor cell based on the channelestimate and weights use for the precoding for the at least onesynchronization signal; and performing detection for the at least onesynchronization signal based on the effective channel estimate torecover the overload indicator for the neighbor cell.
 25. The method ofclaim 22, further comprising: determining loading of the neighbor cellbased on the overload indicator; and controlling operation of the UEbased on the loading of the neighbor cell.
 26. The method of claim 25,wherein the controlling operation of the UE comprises adjusting transmitpower of the UE, or skipping one or more transmissions by the UE, oravoiding transmission on one or more resources by the UE, or acombination thereof.
 27. The method of claim 22, further comprising:determining feedback information based on the overload indicator for theneighbor cell; and sending the feedback information to a serving cell.28. An apparatus for wireless communication, comprising: means forreceiving a reference signal from a neighbor cell at a user equipment(UE); and means for receiving at least one synchronization signal fromthe neighbor cell at the UE, the at least one synchronization signalcomprising an overload indicator for the neighbor cell.
 29. Theapparatus of claim 28, further comprising: means for deriving a channelestimate for the neighbor cell based on the reference signal; and meansfor performing detection for the at least one synchronization signalbased on the channel estimate to recover the overload indicator for theneighbor cell.
 30. The apparatus of claim 28, wherein the at least onesynchronization signal is transmitted with precoding and the referencesignal is transmitted without precoding, the apparatus furthercomprising: means for deriving a channel estimate for the neighbor cellbased on the reference signal; means for deriving an effective channelestimate for the neighbor cell based on the channel estimate and weightsuse for the precoding for the at least one synchronization signal; andmeans for performing detection for the at least one synchronizationsignal based on the effective channel estimate to recover the overloadindicator for the neighbor cell.
 31. The apparatus of claim 28, furthercomprising: means for determining loading of the neighbor cell based onthe overload indicator; and means for controlling operation of the UEbased on the loading of the neighbor cell.
 32. A method for wirelesscommunication, comprising: receiving a first transmission of at leastone synchronization signal from a neighbor cell in a first time periodat a user equipment (UE); and receiving a second transmission of the atleast one synchronization signal from the neighbor cell in a second timeperiod at the UE, the second transmission of the at least onesynchronization signal comprising an overload indicator for the neighborcell.
 33. The method of claim 32, further comprising: deriving a channelestimate for the neighbor cell based on the first transmission of the atleast one synchronization signal; and performing detection for thesecond transmission of the at least one synchronization signal based onthe channel estimate to recover the overload indicator for the neighborcell.
 34. An apparatus for wireless communication, comprising: means forreceiving a first transmission of at least one synchronization signalfrom a neighbor cell in a first time period at a user equipment (UE);and means for receiving a second transmission of the at least onesynchronization signal from the neighbor cell in a second time period atthe UE, the second transmission of the at least one synchronizationsignal comprising an overload indicator for the neighbor cell.
 35. Theapparatus of claim 34, further comprising: means for deriving a channelestimate for the neighbor cell based on the first transmission of the atleast one synchronization signal; and means for performing detection forthe second transmission of the at least one synchronization signal basedon the channel estimate to recover the overload indicator for theneighbor cell.
 36. A method for wireless communication, comprising:determining resources reserved for transmitting an overload indicatorfor a neighbor cell; and receiving the overload indicator for theneighbor cell on the reserved resources at a user equipment (UE). 37.The method of claim 36, further comprising: receiving at least onesynchronization signal transmitted by the neighbor cell with precoding,wherein the overload indicator is transmitted by the neighbor cell withprecoding; deriving a channel estimate for the neighbor cell based onthe at least one synchronization signal; and performing detection basedon the channel estimate to recover the overload indicator for theneighbor cell.
 38. The method of claim 36, further comprising: receivinga reference signal from the neighbor cell; deriving a channel estimatefor the neighbor cell based on the reference signal; and performingdetection based on the channel estimate to recover the overloadindicator for the neighbor cell.
 39. The method of claim 36, wherein thereceiving the overload indicator for the neighbor cell comprisesreceiving a subset of all transmissions of the overload indicator forthe neighbor cell to reduce reception time for the UE.
 40. An apparatusfor wireless communication, comprising: means for determining resourcesreserved for transmitting an overload indicator for a neighbor cell; andmeans for receiving the overload indicator for the neighbor cell on thereserved resources at a user equipment (UE).
 41. The apparatus of claim40, further comprising: means for receiving at least one synchronizationsignal transmitted by the neighbor cell with precoding, wherein theoverload indicator is transmitted by the neighbor cell with precoding;means for deriving a channel estimate for the neighbor cell based on theat least one synchronization signal; and means for performing detectionbased on the channel estimate to recover the overload indicator for theneighbor cell.
 42. The apparatus of claim 40, further comprising: meansfor receiving a reference signal from the neighbor cell; means forderiving a channel estimate for the neighbor cell based on the referencesignal; and means for performing detection based on the channel estimateto recover the overload indicator for the neighbor cell.
 43. A methodfor wireless communication, comprising: receiving a low reuse channel ora broadcast channel from a neighbor cell at a user equipment (UE); andprocessing the low reuse channel or the broadcast channel to recover anoverload indicator for the neighbor cell.
 44. An apparatus for wirelesscommunication, comprising: means for receiving a low reuse channel or abroadcast channel from a neighbor cell at a user equipment (UE); andmeans for processing the low reuse channel or the broadcast channel torecover an overload indicator for the neighbor cell.